Dr. Universe: How is wasabi made and where does it come from? – Christian, 12

When you think of wasabi, you might think of that hot green paste people serve up with sushi. Some restaurants put a bit of wasabi on your plate, but it’s usually not real wasabi. It’s actually a mixture of horseradish, mustard, and green dye. Real wasabi is a lot different.

That’s what I found out from my friend Thomas Lumpkin, a plant scientist who studied wasabi as a researcher at Washington State University. Wasabi is a plant that mainly grows in Japan in the cool, running water of mountain streams and springs.

The part of the wasabi plant we eat comes from the stem, or the rhizome, which can be up to about 4 inches wide and 12 inches long. The plant comes in different shades of green, leaf sizes, and shapes, and in more than 20 different varieties.

Wasabi is one of the hardest plants to grow, which also makes it pretty valuable. If you wanted to buy real wasabi at a store, it would probably be about $95 a pound, Lumpkin said.

In nature, wasabi requires just the right environment to grow. It needs a cool climate, but not too cool in the winter. It also needs freshwater all year long and grows best in a bed of gravel. The Pacific Northwest can provide a lot of these conditions, along with some good shade. Lumpkin and some of his students actually helped people in the Northwest learn how to grow wasabi.

Now there are wasabi farms up and running on the coast of Oregon and Canada’s Vancouver Island. Growing wasabi takes a lot of patience. Only a few farms in the U.S. grow wasabi and only a few fine-dining sushi restaurants serve it.

When cooks prepare the wasabi, they shave off a bit of the stem to clean it up. They sometimes use very fine grating tools, called orsoshigane, which are used in Japanese cooking. These tools can grate up stuff a lot finer than the kind of cheese graters we usually find in the kitchen. Finally, they gather these tiny pieces of wasabi stem together. We might eat it with sushi, sashimi, or noodles. The leaves and the part that connects the leaf to the stem, called petioles, can be pickled or dried.

When we grate the wasabi stem, it breaks the plant’s cells and triggers a chemical reaction that gives the vegetable a very powerful flavor. It’s so strong that sometimes vapors will travel into the back of your mouth and up into the nasal cavity. It hits the sinuses and can easily make your eyes water.

Even though we might not be eating real wasabi when we go to a restaurant, the horseradish in the paste can still add extra spice to your meal. And now you know that wasabi is made by grinding up the root of a pretty interesting plant. It probably came from Japan—but there’s also a chance it was grown in the Pacific Northwest.